Obaid Ormur / The Associated PressAfghans burn tires during an anti-U.S. demonstration over burning of Qurans at a US military base, in Muhammad Agha, Logar province south of Kabul, Afghanistan, Saturday, Feb. 25, 2012.

Kabul, Afghanistan -- Protesters angry over Quran burnings by American troops lobbed grenades at a U.S. base in northern Afghanistan and clashed with police and troops in a day of violence that left seven international troops wounded and two Afghans dead.

The attacks were the latest in six days of violence across the country by Afghans furious at the way some Qurans at an American base outside of Kabul were disposed of in a burn pit. The incident has swiftly spiraled out of control leaving dozens of people dead, including four U.S. troops killed by their Afghan counterparts, in a sign of the tenuous nature of the relationship between Afghanistan and the U.S.

Afghan authorities have launched a manhunt across the country for a driver they suspect in the killing of two U.S. military advisers who were shot to death at an Afghan ministry a day earlier. International advisers working at Afghan ministries were recalled out of fears of another attack.

In Kunduz province, thousands of demonstrators started out protesting peacefully but then the group turned violent as they tried to enter the district's largest city, said Amanuddin Quriashi, district administrator. People in the crowd fired on police and threw grenades at a U.S. base on the city outskirts, he said.

Seven NATO troops were wounded and one of the protesters was killed when troops fired out from the U.S. base, Quriashi said. Another demonstrator was killed by Afghan police, he added. Provincial police spokesman Sarwar Hussaini confirmed the casualties.

More than 30 people have been killed in clashes since it emerged Tuesday that copies of the Muslim holy book and other religious materials had been thrown into a fire pit used to burn garbage at Bagram Air Field, a large U.S. base north of Kabul.